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    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    <script>
        //创建Symbol
        let s = Symbol();

        let s1 = Symbol('sss')
        let s2 = Symbol('sss')
        // s1 === s2   false

        let s3 = Symbol.for('aaa')
        let s4 = Symbol.for('aaa')
        //  s3 === s4  true


        /**
         * js 数据类型：
         *      u  -> undefined
         *      s  -> string symbol
         *      o  object
         *      n  null number
         *      b  boolean
         *          function
         */
    </script>
    
</body>
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